“If I want to send a message I’ll use Western Union,” one of the old-time Hollywood moguls is supposed to have shouted when confronted by a script with a socially uplifting “message”. This attitude, which was far from being confined to Hollywood, has resulted in thousands of relentlessly trivial movies that were manufactured rather than created. Depressingly, many of these have been very popular. But when vitally important themes—messages, if you like—have been embodied in believable narratives that audiences can identify with, the much despised mainstream can become high art. This is certainly true of a film on DVD that…